1. Field of the Invention
The present invention relates to a valve-operating system for an internal combustion engine, comprising cam followers which have cam abutment portions abutting against valve-operating cams provided on a camshaft and which are swingably carried in an engine body and operatively connected to engine valves biased in a closing direction by a valve spring, the cam followers being biased in a direction of abutment of the cam abutment portions against the valve-operating cams by resiliently biasing means different from the valve spring.
2. Description of the Related Art
Japanese Patent Application Laid-open 2004-36560 discloses a lift-variable valve-operating system in which a pair of link arms are turnably connected, each at one end thereof to a cam follower, one of the link arms being turnably carried at the other end thereof by a stationary support shaft, and the other link arm being turnably carried at the other end thereof by a movable support shaft having an axis parallel to the stationary support shaft, in order to continuously change the valve-opening lift amount of an engine valve. In this valve-operating system, the one link arm and the cam follower are resiliently biased in a direction of abutment of a cam abutment portion of the cam follower against a valve-operating cam of a camshaft by a torsion spring surrounding the stationary support shaft. Also, Japanese Patent Application Laid-open 11-81947 discloses a valve-operating system in which the operational characteristic of an engine valve can be changed, and a cam follower is biased by a compression coil spring in a direction of abutment of a cam abutment portion against a valve-operating cam of a camshaft.
However, in the lift-variable valve-operating system disclosed in Japanese Patent Application Laid-open 2004-36560,a space for disposition of the torsion spring is relatively large in a direction along the axis of the stationary support shaft, so that the space for disposition of the torsion spring cannot be secured in some cases in terms of reduction in size of the internal combustion engine. Also, as disclosed in Japanese Patent Application Laid-open 11-81947, even if the valve-operating system is designed so that the cam follower is biased by the compression coil spring in such a manner that the cam abutment portion is brought into abutment against the valve-operating cam, it may be difficult in some cases to dispose the compression coil spring, because the compression coil spring interferes with a member disposed around the cam follower.